Electronic devices, such as cellular telephones, have become increasingly popular. Those devices that are compatible with a large number of accessories have a commercial advantage. Accessories are used in association with the device to increase the functionality thereof. Accessories are attached to the device via an accessory connector thereof. One such accessory connector is the standardized eight pin J3-type accessory connector used in MicroTAC.TM. cellular telephones manufactured and sold by Motorola, Inc. from 1989 to the present. The J3-type accessory connector has an external power supply pin; an audio in pin; an audio out pin; data pins for high speed data communications according to the three-wire bus protocol used in radiotelephone products by Motorola, Inc.; and two ground pins in a predetermined arrangement.
To be compatible with the J3-type accessory connector, an accessory must have a connector that is designed to mate with the accessory connector and have the same number and arrangement of pins. To communicate its identity to the device, the accessory includes a logic circuit or microcontroller capable of driving high speed data communications on the data pins according to the three-wire bus protocol. Unfortunately, such logic circuits or microcontrollers are expensive and oftentimes double the cost of the accessory. Therefore, what is needed is a low cost apparatus and method of identifying an accessory to a device that maintains backward compatibility with existing accessories that use the accessory connector.